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A worm gear, or '''worm wheel''', is a type of Gear that engages with a worm to greatly reduce Rotational Speed , or to allow higher Torque to be transmitted. The image shows a section of a gear box with a bronze worm gear being driven by a worm. A Gearbox designed using a worm and worm-wheel will be considerably smaller than one made from plain spur gears, it also will have its drive axes at 90 ° to each other. With a ''single start'' worm, for each complete turn of the worm the worm-gear advances only one tooth of the gear, so regardless of the worms size (sensible engineering limits notwithstanding), the gear ratio is determined by the ''size of the worm gear:1''.
features worm gears as tuning mechanisms]] Unlike ordinary gear trains, the direction of transmission (input shaft vs output shaft) is not reversible, due to the greater friction involved between the worm and worm-wheel, when a single start (one spiral) worm is used. This can be an advantage when it is desired to eliminate any possibility of the output driving the input. If a multistart worm (multiple spirals) then the ratio reduces accordingly and the ''braking effect'' of a worm and worm-gear may need to be discounted as the gear may be able to drive the worm. Worm gears are a compact, efficient means of substantially decreasing speed and increasing torque. Small Electric Motor s are generally high speed and low torque, the addition of a worm and worm-wheel increases the range of applications that it may be suitable for, especially when the worm gears compactness is considered. Worm-drives have also been used in a few automotive differentials. The worm-wheel carries the differential gearing. This protects the vehcile against rollback but has largely fallen from favour due to their higher than necessary reduction ratios. Torsen differentials use worm-gears and planetry worm-wheels in place of the bevel gearing in conventional open Differential s. SEE ALSO |
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